The SOB format was created by the Serviio developer for use with Serviio. It's not an available format for other devices. Depending on what's in your m3u playlist, they may not be compatible with Serviio online source requirements. Remember that playlists are typically used for local media, not online resources.

Basically the SOB format tells the Serviio console what type of online resource the entry is (Web Resource, RSS or Live Feed), the media type (video, audio or image), the source URL and the display name. Basically, it just auto-populates the same fields you would use in the console for entering a single resource.